Step 6 Then I created another Action. I deleted the brightly coloured layer and the line layer, and saved the result as a PNG in a new folder for the mattes. I closed the image, selecting Don’t Save when asked whether the original artwork should be retained. Then I stopped recording the Action.

I then worked through the rest of the frames by loading them in chunks as separate files, applying the first Action, painting the matte and then applying the second Action – leaving me ready to work on the next frame.

Step 7 Once I was done matting, I took the images and imported them as sequences into a new After Effects composition. Be sure to interpret the footage at the correct frame rate – in this case 12fps. To do this, select the footage in the Project window and press Cmd/Ctrl + Shift + G.

Step 8 I layered together all the footage in the right order, from top to bottom: ‘upper dog’, ‘upper dog matte’, ‘ripple’ and ‘lower dog’. I parented everything to the ‘lower dog’ layer, so when I rotated and scaled it to fit the composition nicely, the rest of the layers followed suit.